Circuit arrangement for the determination of the constant speed rotation of a disklike record medium

Abstract

A circuit arrangement for a flexible magnetic disk drive having an index sensor for optically sensing an index hole defined eccentrically in the magnetic disk, with the index sensor putting out an electric index pulse of less than a predetermined duration each time it detects the index hole during the rotation of the magnetic disk. The index sensor is prone to put out invalid pulses of not less than the predetermined duration as a result of the displacement of the magnetic disk relative to the index sensor. For detecting the constant speed rotation of the magnetic disk on the basis of the valid index pulses only, the circuit arrangement comprises an index pulse spacing detector circuit for producing an index pulse spacing signal indicative of whether the spacings between the successive index sensor output pulses are less than a predetermined limit or not, a latching circuit for putting out a constant speed rotation signal in response to the index pulse spacing signal when the spacing between any two consecutive index sensor output pulses is less than the predetermined limit, and an index pulse duration detector circuit for inhibiting the production of the constant speed rotation signal by the latching circuit upon detection of an invalid pulse even if the spacing between this invalid pulse and the next index sensor output pulse is less than the predetermined limit.

We claim: 
     
       1. In an apparatus for data transfer with a disklike record medium such as a flexible magnetic disk which is rotated at a predetermined constant speed during data transfer, a system for detecting the rotation of the record medium substantially at the constant speed, comprising: (a) an index sensor disposed adjacent a predetermined path of an index mark rotatable with the record medium for generating a valid index pulse of less than a predetermined duration each time the index sensor senses the index mark during the rotation of the record medium, so that the time spacing of the valid index pulses represents the speed of rotation of the record medium, there being the possibility, due for example to the mishandling of the record medium, of the index sensor generating invalid index pulses of not less than the predetermined duration; and   (b) a constant speed detector circuit connected to the index sensor for discriminating between the valid and invalid output pulses of the index sensor and for putting out a constant speed signal when at least two valid index pulses are supplied consecutively with less than a predetermined time spacing representative of the roation of the record medium substantially at the constant speed.   
     
     
       2. In an apparatus for data transfer with a disklike record medium such as a flexible magnetic disk which has an index hole defined eccentrically therein and which is rotated at a predetermined constant speed during data transfer, a system for detecting the rotation of the record medium substantially at the constant speed, comprising: (a) an index sensor comprising a light source and a photodetector fixedly mounted on the opposite sides of the record medium for photoelectrically sensing the index hole in the record medium, the index sensor generating a valid index pulse of less than a predetermined duration each time the index sensor senses the index hole during the rotation of the record medium, so that the time spacing of the valid index pulses represents the speed of rotation of the record medium, there being the possibility of the index sensor generating invalid index pulses of not less than the predetermined duration as when the record medium is displaced relative to the index sensor at the time of loading of the record medium in the apparatus; and   (b) a constant speed detector circuit connected to the index sensor for discriminating between the valid and invalid output pulses of the index sensor and for putting out a constant speed signal when at least two valid index pulses are supplied consecutively with less than a predetermined time spacing representative of the rotation of the record medium substantially at the constant speed.   
     
     
       3. In an apparatus for data transfer with a disklike record medium such as a flexible magnetic disk which is rotated at a predetermined constant speed during data transfer, a system for detecting the rotation of the record medium substantialy at the constant speed, comprising: (a) an index sensor disposed adjacent a predetermined path of an index rotatable with the record medium for generating a valid index pulse of less than a predetermined duration each time the index sensor senses the index during the rotation of the record medium, so that the time spacing of the valid index pulses represents the speed of rotation of the record medium, there being the possibility, due for example to the mishandling of the record medium, of the index sensor generating invalid index pulses of not less than the predetermined duration;   (b) an index pulse spacing detecting circuit coupled to the index sensor for putting out a constant speed signal when at least two valid index pulses are supplied consecutively with less than a predetermined time spacing representative of the rotation of the record medium substantially at the constant speed; and   (c) an index pulse duration detecting circuit having an input coupled to the index sensor and an output coupled to the index pulse spacing detecting circuit for preventing the latter from putting out the constant speed signal when at least one of two consecutive output pulses of the index sensor has a duration of not less than the predetermined limit even though the time spacing therebetween may be less than the predetermined time spacing.   
     
     
       4. In an apparatus for data transfer with a disklike record medium such as a flexible magnetic disk, wherein an index sensor is disposed adjacent a predetermined path of an index rotatable with the record medium for generating a valid index pulse with a duration of less than a predetermined limit, each time the index sensor senses the index during the rotation of the record medium, so that the time spacing of the valid index pulses represents the speed of rotation of the record medium, there being the possibility, due for example to the mishandling of the record medium, of the index sensor generating invalid pulses having durations of not less than the first predetermined limit, a circuit arrangement for detecting the constant speed rotation of the record medium from the time spacing of the valid index pulses in the face of the invalid output pulses of the index sensor, comprising: (a) a source of clock pulses;   (b) a counter circuit responsive to the leading edge of each valid or invalid outpout pulse of the index sensor for restarting the counting of the clock pulses;   (c) an index pulse spacing detector circuit responsive to the successive counts of the counter circuit for producing an index pulse spacing signal indicative of whether or not the time spacings between the successive valid or invalid output pulses of the index sensor are less than a second predetermined limit which represents the rotation of the record medium substantially at the constant speed;   (d) a latching circuit responsive to the index pulse spacing signal for putting out a constant speed rotation signal by latching the index pulse spacing signal when the time spacing between at least two consecutive output pulses of the index sensor is less than the second predetermined limit, the constant speed rotation signal being indicative of the rotation of the record medium substantially at the constant speed; and   (e) an index pulse duration detector circuit responsive to the successive counts of the counter circuit for delivering to the latching circuit an index pulse duration signal indicative of whether each output pulse of the index sensor has a duration of less than the first predetermined limit or not, the index pulse duration signal being effective to inhibit the latching action of the latching circuit, and hence the production of the constant speed signal thereby, when any one output pulse of the index sensor has a duration of not less than the first predetermined limit even if the time spacing between this invalid pulse and the next output pulse of the index sensor is less than the second predetermined limit;   (f) whereby the latching circuit is permitted to produce the constant speed rotation signal only when at least two valid index pulses are generated consecutively by the index sensor with a time spacing less than the second predetermined limit.   
     
     
       5. The circuit arrangement of claim 4 wherein the counter circuit comprises: (a) a differentiating circuit coupled to the index sensor; and   (b) a binary counter having a clock input coupled to the clock pulse source and a reset input coupled to the differentiating circuit.   
     
     
       6. The circuit arrangement of claim 5 wherein the binary counter has a plurality of output terminals for providing outputs indicative of the counts of the clock pulses, and wherein the index pulse spacing detector circuit comprises a gate having input ports coupled to selected ones of the output terminals of the binary counter. 
     
     
       7. The circuit arrangement of claim 6 wherein the index pulse duration detector circuit comprises a second gate having input ports coupled to selected ones of the output terminals of the binary counter, the second gate having an additional input port coupled to the index sensor. 
     
     
       8. The circuit arrangement of claim 7 wherein the latching circuit comprises: (a) a positive power supply;   (b) a first D flip flop having a data input coupled to the positive power supply, a clock input coupled to the differentiating circuit, and a reset input coupled to the first recited and second gates; and   (c) a second D flip flop having a data input coupled to a noninverting output of the first flip flop, a clock input coupled to the differentiating circuit, and a reset input coupled to an inverting output of the first flip flop, the second flip flop putting out the constant speed rotation signal.   
     
     
       9. The circuit arrangement of claim 4 wherein the first predetermined limit is approximately eight milliseconds.